A variety of electronic and optoelectronic devices can be enabled by developing, for example, high quality III-V semiconductors on elemental silicon (Si) substrates or IV semiconductors on Si substrates. Surface layers capable of achieving the performance advantages of III-V or IV materials may host a variety of high performance electronic devices such as CMOS and quantum well (QW) transistors fabricated from extremely high mobility materials such as, but not limited to, indium antimonide (InSb), indium arsenide (InAs), germanium (Ge), and silicon germanium (SiGe). Optical devices such as lasers, detectors and photovoltaics may also be fabricated from various other direct band gap materials, such as, but not limited to, gallium arsenide (GaAs) and indium gallium arsenide (InGaAs). These devices can be further enhanced by monolithically integrating them with conventional devices of Si since use of a Si substrate has the additional advantage of cost reduction.
The growth of III-V and IV materials upon Si substrates, however, presents many challenges. Crystal defects are generated by lattice mismatch, polar-on-nonpolar mismatch, and thermal mismatch between the III-V semiconductor epitaxial (EPI) layer and the Si semiconductor substrate or the IV semiconductor EPI layer and the Si semiconductor substrate. When the lattice mismatch between the EPI layer and substrate exceeds a few percent, the strain induced by the mismatch becomes too large and defects are generated in the EPI layer by relaxing the EPI film. Once the film thickness is greater than the critical thickness (i.e., film is fully strained below this thickness and partially relaxed above this thickness), the strain is relaxed by creating misfit dislocations at the film and substrate interface as well as in the EPI film. The EPI crystal defects may be in the form of threading dislocations, stacking faults and twins. Many defects, particularly threading dislocations and twins, tend to propagate into the “device layer” where the semiconductor device is fabricated. Generally, the severity of defect generation correlates to the amount of lattice mismatch between the III-V semiconductor and the Si substrate or the IV semiconductor and the Si substrate.